For many components, castings in particular, material removal subsequently needs to be carried out for instance to four indentations or through-holes need. Particularly for turbine components which have film cooling holes for cooling, holes are subsequently introduced after production of the component.
Such turbine components often also have layers, for example a metallic layer or interlayer and/or a ceramic outer layer. The film cooling holes must then be produced through the layers and the substrate (casting).
U.S. Pat. Nos. 6,172,331 and 6,054,673 disclose a laser boring method for introducing holes into layer systems, ultrashort laser pulse lengths being used. A laser pulse length is found from a particular laser pulse length range and the hole is thereby produced.
DE 100 63 309 A1 discloses a method for producing a cooling air opening by means of the laser, in which the laser parameters are adjusted so that material is ablated by sublimation.
U.S. Pat. No. 5,939,010 discloses two alternative methods for producing a multiplicity of holes. In one method (FIGS. 1, 2 of the US patent) one hole is initially produced fully before the next hole is produced. In the second method, the holes are produced stepwise, by first producing a first subregion of a first hole then a first subregion of a second hole etc. (FIG. 10 of the US patent). Different pulse lengths may be used in the two methods, but the pulse length used in a given method is always the same. The two methods cannot be interlinked.
The cross-sectional area of the region to be ablated always corresponds to the cross section of the hole to be produced.
U.S. Pat. No. 5,073,687 discloses the use of a laser for producing a hole in a component, which is formed by a substrate with a copper layer on both sides. Initially a hole is produced through the copper film by means of a longer pulse duration, and then a hole is produced by means of shorter pulses in the substrate consisting of a resin, a hole subsequently being produced through a copper layer on the rear side with a higher output power of the laser. The cross-sectional area of the region to be ablated corresponds to the cross section of the hole to be produced.
U.S. Pat. No. 6,479,788 B1 discloses a method for producing a hole, in which longer pulses are used in a first step than in a further step. The pulse duration is varied here in order to produce an optimal rectangular shape in the hole. The cross-sectional area of the beam is also increased as the pulse length decreases.
Another laser boring method is disclosed in EP 1 062 070 B1.
The use of such ultrashort laser pulses is expensive and very time-intensive owing to their low average powers.